JP6129187B2 - Bulk wave resonators based on micromachined vertical structures - Google Patents

Description

  The present invention relates to a planar bulk wave resonator of a plane-planar, i.e., a piezoelectric material having a metallized plane, and a method for manufacturing such a resonator.

  Bulk wave resonators are widely used in multiple applications such as strong coupling filters, high frequency resonators, temperature sensors, acceleration sensors, gyrometers, torque sensors, gravimetric sensors, acousto-optic modulators with strong confinement and strong modulation Is done.

  The search for a method for collectively manufacturing a large number of bulk wave resonators on a single crystal flat plate remains a topic of concern.

  The method developed so far essentially consists of using a method for rough polishing / polishing a flat plate that is optionally affixed flat to a support substrate.

  This approach is undoubtedly strong and efficient, but the plate thickness of less than 10 μm cannot be easily controlled.

Toshiaki Suhara, Shuji Fujiwara, and Hiroshi Nishihara, "Proton-exchanged Fresnel lenses in TiLiNbO3 waveguides", Applied Optics, Vol. 25, Issue 19, 3379-3383 (1986). Arnaud Grisard, “Laser guides d'ones dans le niobate de lithium doi en ti nium, dolphin i nium, dop ed i nium, dop ed i nium, dop ed i ti n i s i n i ti n i s i n i n i n i i n i i n e n i e n i um i n i s i n i n i n i n i n i n e n i n e n i um e n i um i F. R. Face des Sciences, 1997

  Therefore, the technical problem is to improve the production of flat plates with a thickness of less than 10 μm, in other words by improving the production yield of planar-planar bulk wave resonators on the same single crystal wafer. is there.

  In connection therewith, another technical problem is also to improve the integration of several bulk-wave resonators of the plane-planar type on the same single crystal wafer.

To this end, an object of the present invention is to provide a substrate block as a holding means, which has a plane that operates at a predetermined frequency and that has a first thickness e1 along the plane normal and is made of a first material. When,
A resonant plate having first and second planes positioned facing each other, having a length L, a width l and a second thickness e2, and comprising a second piezoelectric material;
A bulk wave piezoelectric resonator comprising first and second metal electrodes that at least partially cover a first surface and a second surface of a resonant plate, respectively, and are positioned at least partially facing each other through the resonant plate Because
The resonant plate is vertically fixed near the plane of the substrate block such that the width of the resonant plate and the first thickness of the substrate block have the same direction;
The first material, the second material, the first thickness of the substrate block, the length of the resonant plate, the width l, the second thickness capture the bulk wave at the operating frequency of the resonator, and the plane-plane A bulk wave piezoelectric resonator, characterized in that it is configured to produce a bulk wave piezoelectric resonator of the type, i.e. a type of bulk wave propagating in the direction of the thickness of the resonant plate.

According to certain embodiments, the resonator includes one or more of the following features.
The transverse form factor Fl, defined as the ratio of the resonance plate width l to the resonance plate second thickness e2, is 5 or more, preferably 10 or more.
The longitudinal form factor, defined as the ratio of the length of the resonant plate to the thickness of the resonant plate, is 5 or more, preferably 10 or more.
The resonant plate and the substrate block are made of the same piezoelectric material and together form the part;
The resonator comprises an attachment and / or acoustic insulation element of an operating frequency f different from the substrate block and the resonance plate, consisting of at least one third material different from the first and second materials, The acoustic insulation elements are included in the group formed by a Bragg mirror formed by a single adhesive layer, a stack of layers with contrasting acoustic impedance.
The resonant plate and the substrate block are made of the same piezoelectric material;
The crystallographic cutting of the resonant plate along a plane parallel to the two surfaces indicates that the electroacoustic coupling coefficient of the transducer formed by the resonant plate is 0.0001 for bulk waves propagating in the thickness direction of the resonant plate. Is selected to be larger.
The resonant plate has a contraction region throughout its length in the thickness direction, so that the thickness of the resonance plate passes through a minimum amount and when the resonant plate is attached to the substrate block, the contraction region Is located near the plane of the substrate block.
The first material is formed by lithium niobate, lithium tantalate, potassium niobate, piezoelectric ceramic, quartz, lithium tetraborate, gallium orthophosphate, langasite, langate, langanite, zinc oxide and aluminum nitride Included in material set.
-The second material is formed by lithium niobate, lithium tantalate, potassium niobate, piezoelectric ceramic, quartz, lithium tetraborate, gallium orthophosphate, langasite, langate, langanite, diamond carbon, silicon, sapphire Included in a set of materials.
-The metal electrode is made of a material included in a set of materials formed by aluminum, copper, titanium, platinum, iridium, zirconium, rubidium, molybdenum, nickel, tungsten, gold, polysilicon, alloys of these different metals. ,
Their thickness is distributed to obtain a mass distribution localized at the boundary between the resonant plate and the substrate block in order to capture and collect bulk waves within the local region of the resonant plate.

The object of the present invention is also a method for manufacturing a bulk wave resonator operating at a predetermined frequency in the following steps:
The step of preparing the initial resonant flat plate raw layer, wherein the initial resonant flat plate raw layer is made of a piezoelectric material, the raw layer thickness eb, and the thickness of the raw layer in a plane perpendicular to the thickness direction; The crystal orientation of the raw layer is pre-selected so that the crystallographic cut surface of the raw layer is in the direction of the thickness eb, so that the crystal orientation of the raw layer is clearly greater than A wafer cut along the plane and having a thickness e2 results in a plane-to-plane piezoelectric resonator of the type in which bulk waves propagate in the thickness direction of the wafer with an electroacoustic coupling coefficient of 0.0001 or more. Let the steps and
A resonant plate having a resonant plate thickness e2, first and second planes positioned facing each other, in the thickness direction of the raw layer and partially or entirely in the initial resonant plate raw layer; A step of cutting, the plane having a length L and a width l, and the cutting is performed by a machining method along the cut surface direction, and the width l of the flat plate and the thickness of the raw layer are In the same direction, the material and crystal orientation of the raw layer, the direction of the cut plane, the length L, the width l, and the second thickness of the resonant plate capture the bulk wave at the operating frequency of the resonator and A planar type, i.e. configured to produce a bulk wave piezoelectric resonator of the type in which the bulk wave propagates in the direction of the thickness of the resonant plate;
-Depositing first and second metal electrodes at least partly covering the first side and the second side of the resonant plate respectively and at least partly facing each other. .

According to certain embodiments, the manufacturing method includes one or more of the following features.
The step of partially cutting the resonant flat plate in the thickness direction of the initial raw layer and the initial resonant flat plate, the partial cutting in the thickness direction of the raw layer being a flat plate through the first surface; Removing the first bar adjacent to the plate and the second bar adjacent to the flat plate through the second surface;
Holding the flat plate and having a reference plane so as to obtain the resonant flat plate and the substrate block as the rest of the raw layer after cutting the bar-like portion, the flat plate being integrally attached perpendicularly to the plane of the substrate block; The width l of the flat plate is therefore the height of the flat plate relative to the substrate block.
Providing a holding substrate raw layer having a holding substrate raw layer thickness and comprising a substrate material;
The operating frequency different from the substrate raw layer and the resonant flat plate raw layer, which is composed of at least one third material different from the substrate raw layer material and the resonant flat plate raw layer between the holding substrate layer and the flat plate raw layer. Positioning at least one layer intended to form an adhesion and / or acoustic insulation element, wherein the at least one raw layer forming the adhesion and / or acoustic insulation element is a single bond Included in the group formed by the Bragg mirror formed by the agent layer, a stack of layers having contrasting acoustic impedances;
Cutting at least a flat plate unprocessed layer over a certain depth to form a resonant flat plate.
The step for cutting out the resonant plate is achieved by sawing.

  The invention will be better understood by reading the following description of several embodiments that are given only by way of example and made with reference to the drawings.

1 is a diagram of a first embodiment of a bulk wave resonator in which a substrate block and a resonant plate are integrated. FIG. FIG. 2 is a cross-sectional view of the resonator of FIG. 1 in the direction of the thickness of the resonant plate along section line II-II of FIG. It is sectional drawing in the thickness direction of the resonant flat plate of 2nd Embodiment derived from the bulk wave resonator of FIG. 1 in which a bottleneck separates a flat plate from a substrate block. FIG. 6 is a cross-sectional view in the thickness direction of a resonant plate of a third embodiment of a resonator derived from the resonator of FIG. 1 applying increased metallization to the electrodes on top of the substrate. FIG. 6 is a cross-sectional view in the thickness direction of a resonant plate of a fourth embodiment of a bulk wave resonator having the same geometric shape as that of the resonator of FIG. 1, wherein the attachment element connects the resonant plate to the substrate block. . FIG. 5 is a cross-sectional view in the thickness direction of a resonant plate of a fifth embodiment of a bulk wave resonator having an acoustic insulation element connecting the resonant plate to the substrate block and having the same geometric shape as that of the resonator of FIG. is there. 2 is a flowchart of a method for manufacturing the resonator of FIG. FIG. 8 is a diagram of a first intermediate state of the resonator of FIG. 1 manufactured by the method of FIG. FIG. 8 is a diagram of a second intermediate state of the resonator of FIG. 1 manufactured by the method of FIG. FIG. 8 is a diagram of a third intermediate state of the resonator of FIG. 1 manufactured by the method of FIG. FIG. 7 is a diagram of a chip integrating several resonator sets described in FIGS. 1 to 6 on the same substrate. 7 is a flow diagram of a method for manufacturing the resonator of FIG. 5 or FIG. 6. FIG. 13 is a diagram of a first intermediate state of the resonator of FIG. 5 or FIG. 6 manufactured by the method of FIG. FIG. 13 is a diagram of a second intermediate state of the resonator of FIG. 5 or FIG. 6 manufactured by the method of FIG. FIG. 13 is a diagram of a third intermediate state of the resonator of FIG. 5 or FIG. 6 manufactured by the method of FIG. 4 is a flowchart of a manufacturing method that generalizes manufacturing methods 7 and 12;

  According to FIGS. 1 and 2, the bulk acoustic wave resonator 2 having a piezoelectric excitation mode, which is configured to operate at a predetermined desired frequency f, includes a substrate block 4 and first and second surfaces 8 and 2 facing each other. And a first metal electrode 12 deposited on the first surface 8 of the resonant plate 6 and a second metal electrode 14 deposited on the second surface 10.

  The substrate block 4 made of the first material includes a plane 16, has a first thickness e 1 along the normal of the plane 16, and is used as a support for the resonant plate 6.

  The resonant plate 6 made of the second piezoelectric material is bounded by the first and second planes 12 and 14. Both sides 12, 14 of the flat plate 6 are parallel to each other and spaced by a distance indicated by e 2, which distance forms the thickness of the resonant flat plate 6.

  Each surface 12, 14 of the resonant flat plate 6 has a length L, a width l, and a second thickness e2.

  Here, the first material and the second material are the same. For example, the first and second materials are lithium niobate.

  1 and 2, the resonance plate 6 and the substrate block 4 are integrally formed as a single component.

  The first and second metal electrodes 12 and 14 at least partially cover the first surface 8 and the second surface 10 of the resonance plate 6, respectively. In order to achieve bulk wave excitation within the resonant plate 6, at least a portion of the surface of both electrodes 12, 14 is superimposed through the plate 6.

  The underlying idea leading to the design of the resonator of FIG. 1 is according to the lateral dimensions, ie here the thickness of the substrate, in order to produce a resonator in the form of a plate or rod that is attached perpendicularly to the substrate. , Consisting of thinning the raw substrate block, which has an overall rectangular parallelepiped initial shape and surrounds the flat plate, in some way.

  According to this idea, all cuts of crystalline piezoelectric material that may be used for bulk wave applications are in a crystal orientation where the reference crystal orientation for application to the resonator is defined by the extension planes on both sides of the resonant plate. It may be used given that there is.

  Here, according to FIGS. 1 and 2, by way of example, the resonant plate is a raw substrate pre-cut along a lithium niobate cut known as (YX1) / 128 ° and was revised in 1949 Cut along a cut known as (YX1) / 38 ° according to the IEEE Std-176 standard. Cutting out the resonant plate is performed assuming that electrical excitation is applied between both sides of the plate and the propagation direction of the bulk wave is directed along the normals of the two sides of the plate. The flat plate has a thickness e2 of 5 μm and a width l of 25 μm.

Cutting the raw substrate (YXl) / 128 °, on the one hand, because of its availability as it is a standard for lithium niobate, and its orthogonal cutting (YXl) / 38 ° is particularly preferred for bulk waves It is selected because it is close to (YXl) / 36 °. For this cut (YXl) / 36 °, only the longitudinal mode is coupled with a maximum electromechanical coupling k _s ² of 20%.

  Thereby, the microfabricated flat plate on the lithium niobate cut (YX1) / 128 ° forming the substrate thus intentionally adds or pulls a rotation of 90 ° to cut (YX1) / 38 °, ie 128 ° Equivalent to the configuration of a bulk wave resonator on the cut of the design, it puts us in close proximity to the optimal value of (YX1) / 36 °.

  The associated structure is useful within the application of the resonator when the plate form factor indicated by Fl and equal to the ratio of the plate width l to the second thickness has a small value here equal to 5. It should be noted that the parasitic mode at 660 MHz has a significant disadvantage with a low quality factor that disrupts all the associated longitudinal modes.

  There are several solutions to improve this situation.

  The first solution consists in extending the width l of the plate to facilitate the establishment of a useful resonant longitudinal mode between both sides and to minimize the portion of acoustic energy near the substrate block.

  This solution has been found to be very effective, and better results have been found, for example, in terms of longitudinal mode resonance with very well resolved and very pure spectral response, for example the form factor Fl Obtained in this case, corresponding to a thickness e2 of 5 μm and a width l of 75 μm.

  For this higher form factor, the electromechanical coupling is always 19% and the quality factor increases for the longitudinal mode.

  When the form factor Fl is even higher, for example equal to 200, the spectral purity of the resonator is improved. For substrate blocks with a lithium niobate cut along the cut YXlt / 126 ° / 90 °, a particular outstanding resonance with a bond slightly greater than 20% is obtained.

  Therefore, when the form factor Fl is sufficiently high, the quality factor of the resonance is limited only by the intrinsic properties of the material forming the resonant plate alone, and not by the effects of losses due to acoustic radiation at the substrate block. .

  The second material constituting the resonant plate is a material formed of lithium niobate, lithium tantalate, potassium niobate, piezoelectric ceramic, quartz, lithium tetraborate, gallium orthophosphate, langasite, langate, langanite Included in the pair.

  Alternatively, the piezoelectric material of the resonant plate, its crystallographic cut and its thickness make it possible to generate and maintain a bulk wave from the plate that propagates with transverse polarization in the thickness direction of the plate. Selected to do.

  As an example, when using quartz AT cutting known as (YX1) / 36 ° according to the IEEE Std-176 standard revised in 1949, the slicing of the plate is (YX1) / 126 ° or even (YX1 ) / − 54 ° would be performed from a raw quartz block that forms a pre-cut substrate along a cutting slice.

  In general, the resonant plate is vertically attached near the plane of the substrate block such that the width of the resonant plate and the first thickness of the substrate block have the same direction.

  In general, the first material, the second material, the first thickness e1 of the substrate block, the length L, the width l, and the second thickness e2 of the resonant plate 6 are the bulk waves of the operating frequency of the resonator. Captured and configured to produce a bulk-wave piezoelectric resonator of the plane-planar type, i.e., a type in which bulk waves propagate in the thickness direction of the resonant plate.

  In operation, the resonator is connected to the output of the electrical excitation source 20 and the input of a circuit 22 for extracting useful signals at the resonance and operating frequency f, which forms an output load.

  An electrical excitation source 20 connected between the first electrode 12 and the second electrode 14 is configured to generate a voltage signal having a main sine wave component at the operating frequency f.

  The extraction circuit 22 that is also connected between the first electrode 12 and the second electrode 14 is configured to extract a useful signal at the operating frequency f.

  According to FIG. 3, the second embodiment of the resonator 32 derived from the resonator 2 of FIG. 1 includes a resonant plate that is integrally attached to the substrate block.

  The materials and geometric dimensions used for the resonant plate and substrate block are the same as those of the resonator 2 of FIG. 1 in terms of thickness e1, length L and width l.

  The resonant plate, indicated here with reference numeral 36, has a contraction region 38 with the thickness of the plate in the direction of width l over its entire length L.

  In the contraction region 38 located near the plane 16 of the substrate block 4, the thickness of the flat plate 36 varies and passes through a minimum amount.

  The thinning of the flat plate formed by the shrink region 38 used at the base of the resonant flat plate 36 provides the possibility to best insulate the maximum vibration region inside the flat plate 36 attached to the substrate 4.

  In this embodiment, this structure is called a bottleneck structure by analogy with the narrow shape of the bottleneck.

  This structure has been demonstrated for a form factor Fl of 15 as expected for the resonator of FIG. 1, i.e. a flat plate width l of 75 [mu] m for a thickness e2 of 5 [mu] m.

  The first and second electrodes 42, 44 each cover a different surface of the flat plate 36 and fill the recess formed by the contracted region of the flat plate at the bottom of the flat plate.

  According to FIG. 4, the third embodiment of the resonator derived from the resonator 2 of FIG. 1 applies an increased metallization to the electrodes on the top of the substrate.

  In this embodiment, only the first and second electrodes, indicated by reference numerals 54 and 56, respectively, include the different bulges 58, 60, i.e. the addition of metal, in FIG. And 14 and different.

  The electrodes 54, 56 are configured through this addition of metal to capture the mass effect on the top of the substrate and localize the maximum amplitude of acoustic vibration away from the attachment of the plate 6 to the substrate 4.

  Alternatively, this mass effect may also be obtained by doping the top of the substrate. For most single crystal materials, there are doping methods that give the possibility of replacing atoms that are foreign to the crystal structure or even integrating them into the lattice in order to locally alter the properties of the material.

In particular, the method used in optics using lithium niobate involves proton exchange that allows diffusion of light atoms (hydrogen, titanium, etc.) in the crystal lattice with or without structural changes. This method is described, for example, in a paper by Toshiaki Suhara, Shuji Fujiwara and Hiroshi Nishihara, entitled “Proton-exchanged Fresnel lessens in TiLiNbO ₃ waveguides”, Apli. 25, Issue 19, 3379-3383 (1986).

  It is also possible to replace heavier atoms (erbium, MgO, etc.) in the crystal lattice by high temperature diffusion. Such a method is entitled "Las guides in arium and dop ed sir eu n, ar s ar n ar n ar n ar n ar n ar n ar n ar n ar n ar n ar n ar n of ar s ar n ar n ar n ar n ar n ar n, F. R. Facial des Sciences, 1997. Therefore, it is possible to locally change the elastic properties by changing the mass density and thus create the required guiding conditions depending on the selected crystal orientation.

  According to FIGS. 5 and 6, other structures of the resonator allow for improved bulk wave capture at the resonant plate.

  According to FIG. 5, the fourth embodiment of the resonator 62 includes a substrate block 64 and a resonance plate 66 made of different materials.

  The material of the resonance plate 66 has piezoelectric characteristics.

  The shapes and geometric dimensions of the substrate block 64 and the flat plate 66 are the same as those of the substrate block 4 and the resonant flat plate 6 of FIG.

  According to FIG. 5, the substrate block 64 and the resonant plate 66 are separate components that are connected to each other through a coupling element 68, such as an acoustically transparent adhesive joint here. The adhesive joint is deposited on a polymer layer that is deposited and cross-linked, for example, by centrifugation, to create a solid bond between the material of the flat plate 66 and the material of the substrate block 64, or further on the surface to be adhesively bonded. Metal layers used for transport by intermetallic diffusion, Au, In, Cu being the most commonly used materials for this purpose and these layers are deposited on the sides of the resonant plate 66 As long as the counter electrode is not short-circuited or deposited on the surface to be further bonded and their hydrophilicity applied to a so-called SOI (silicon-on-insulator, trademark SOITEC) substrate May be understood as a silica layer that is activated to enable

  The first material of the substrate block 64 is selected such that the propagation speed of bulk waves propagating therethrough is greater than those of the second material.

  For example, the second material forming the resonant plate 66 may be niobic acid or tantalum deposited on the diamond carbon layer that forms the first material of the substrate block or, if necessary, more easily on silicon or sapphire. Lithium acid, quartz, langasite or any other single crystal piezoelectric material.

  According to FIG. 6, a fifth embodiment of a resonator 72 derived from the resonator of FIG. 5 includes a substrate block 74 and a resonant plate 76 that are identical in material.

  Resonator 72 includes an acoustic isolation element 78 positioned between substrate block 74 and resonant plate 76 and attached to the latter using two adhesive joints not shown in FIG.

  The acoustic isolation element 78 is here a Bragg mirror made using a stack of layers of strongly contrasting acoustic impedance.

  A strongly contrasting acoustic impedance layer is, for example, an aluminum nitride or silicon nitride and silicon oxide layer, and the stack is configured to reflect the bulk wave of the expected operating frequency in phase and completely.

  Alternatively, the first material forming the substrate and the second material forming the flat plate are different.

  The embodiment of FIGS. 5 and 6 includes an attachment and / or acoustic isolation element that differs from the substrate block and the resonant plate, wherein the resonator is composed of at least one third material different from the first material and the second material. And may be generalized by considering that adhesion and / or acoustic insulation elements are included in the group formed by a Bragg mirror formed by a single adhesive layer, a stack of contrasting acoustic impedance layers .

  According to FIG. 7, the complete method 102 for making the resonator of FIG. 1 comprising at least one resonant plate integrally connected to the substrate block and vertically mounted comprises a series of steps 104, 106, 108, 110, 112, 114, and 116 are included.

  The microfabrication step is applicable to any lithium niobate or lithium tantalate cutting.

  Here, the initial raw material of the method is a slice of lithium niobate called a “wafer”.

  In general, under the cover of determining appropriate sawing conditions, the method is applicable to any single crystal material, particularly a piezoelectric material.

  The use of a blade capable of polishing a surface simultaneously with cutting offers the possibility of creating a surface that is compatible with effective bulk wave excitation and reflection in terms of resonance quality. The resulting surface should have a roughness of tens to a few RMS nanometers, ideally optical polishing. In any case, the surface roughness of the resonator greater than 100 nm RMS does not match the quality of the resonance according to the acoustoelectric standard.

  The use of a precision saw, such as a Disco® brand saw, gives the possibility of defining both planes of the plane of the resonator plate with two saw cuts.

  The thickness e2 resolution of the resonator plate is defined by the alignment accuracy between these saw cuts and may reach 1 μm in the best case.

  The width l of the resonant plate is defined in this connection by the required cutting depth in the thickness direction of the substrate block formed by the lithium niobate wafer and can reach several hundred μm.

  In a first step 104, a lithium niobate wafer is prepared so that the initial cut is in the direction of thickness with a first upper surface and a second lower surface,

Known as.

  In a second step 106, the top surface of the lithium niobate wafer is coated with a resin, for example, Shipley brand resin S1828. The resin deposition is carried out for example in a spin-coating type method with a thickness exceeding 2.5 μm. In the same step 106, the resin is crosslinked at 95 ° C. for 1 hour in an oven to evaporate the solvent and thereby make the resin more resistant to the saw cutting step.

  In the third step 108, one plate or several resonant plates are cut thin. In order to construct a flat sawing, here at least four saw cuts are required to make the flat plate. In fact, the width of the saw blade is 200 μm so that two superimposed saw cuts will give an accessible gap of 350-400 μm on both sides of the plate to allow testing under the probe tip. To be done.

  During the third step 108, the thickness e2 and width l of the at least one flat plate is determined by the depth and alignment accuracy of the cut in a series of two saw cuts and the electrode due to the superposition of the two saw cuts. Defined by width.

  Once the third step 108 has been performed, a fourth step 110 includes at least one strip in the longitudinal direction on each free surface at the top of the plate as well as on the floor of the substrate located between the plates. The strip in the length direction is covered with the protective resin S1828.

  In a fifth step 112, metal electrodes are deposited over a length L that can reach several centimeters on the sides, ie the sides of the plate, as well as the bottom of the trench with a width comprised between 350-400 μm. .

  To cover the sides of a flat plate or a series of flat plates, the groove over the width l can reach several hundred μm, and the deposition of aluminum allows the chip formed by the substrate and the flat plate to be, for example, the length L of the flat plate. This is achieved by three sputterings by tilting them by 45 ° twice around an axis pointing in the direction of.

  In this fifth step 112, the entire chip is covered with an aluminum layer and the electrodes are then obtained by the so-called lift-off technique, i.e. peeling. For this purpose, the chip is immersed in a solvent bath (stripping solution), for example stripping solution 1165, and the chemical solution dissolves the protective resin, here resin S1828, heated to 70 ° C. for several hours.

  Lift-off is then accelerated and accomplished by using the ultrasonic bath for 1 minute. This step in particular allows the removal of the resin localized at the top of the plate and the insulation of the electrodes deposited on the opposite surface of the resonant plate.

  Next, in a sixth step 114, the plate or bar is made using a spray coating technique to harden the plate or bar before the seventh step 116 for cutting the resonant plate longitudinally. It is covered with a protective resin S1805. This sixth step 114 gives the possibility to cover the structured niobic acid wafer, ie the chip provided with their electrodes, with a resin.

  The seventh final step 116 consists of defining the length L of the plate or bar by cutting with a saw, for example here in our case 500 mm. This seventh step 116 is quite important and may cause many flat plate breaks and hence losses. In fact, the problem here is that every 500 μm along the direction of the length L and the first cutting depth, ie the plate width l, in order to make all the basic chips formed thereby electrically independent. To produce a saw cut perpendicular to the grooved surface over a greater depth.

  According to FIG. 8, the first intermediate state 202 of the resonator 2 of FIG. 1 obtained at the end of the second step 106 of the method 102 is a stack of a layer 204 of resin S1828 and a raw wafer 206 of lithium niobate 206. It is.

  According to FIG. 9, the second intermediate state 212 of the resonator of FIG. 1 manufactured by method 102, obtained at the end of the third sawing step 108, is a concave or bare or exposed valley 218, 220. A flat plate 26 surrounded on both sides by a machine block includes a machined substrate block. The two end bars 222, 224 of the block 214 now surround only one flat plate 216. The resin layer 226 is deposited on the upper surface 228 of the flat plate, the upper surfaces 230 and 232 of the rod-shaped portions 222 and 224, and the two strip-shaped portions 234 and 236 of the recesses positioned on both sides of the flat plate 216.

  According to FIG. 10, the third intermediate state 242 of the resonator of FIG. 1 produced by the method 102 obtained at the end of the lift-off step 112 for depositing the electrode is a structured chip.

  Here, chip 242 includes a single resonant plate 216 having two electrodes 244, 246 of aluminum on both sides of its two sides, each electrode 244, 246 comprising an upper surface 228 of plate 216 and a resonant plate 216. Slightly protrudes from a portion of the floor surface of the substrate 214 at the bottom of each side.

  This structure after cutting off the edge of the substrate corresponds to the structure of the resonator of FIG.

  According to FIG. 11, a chip 252 forming a complex resonant surface includes three basic resonators 254, 256, 258 formed by different resonant plates 264, 266, 268, respectively. Resonant plates 264, 266, 268 having the same width l have different thicknesses e21, e22, e23.

  The first two resonant plates 264, 266 shown on the left side in FIG. 11 are coupled together by sharing the same electrode 270 made by metal connections deposited on the common substrate floor 272.

  The first two resonant plates 264, 266 are electrically separated from the third plate 268 by an insulating strip 276.

  According to FIG. 12, a complete method 302 for making the resonator of FIG. 5 or FIG. 6 comprising at least one resonant plate that is attached perpendicularly to the substrate block and connected through adhesion and / or acoustic isolation means A series of steps 304, 306, 308, 310, 312, 314, 316, 318, 320.

  Here, the adhesion and / or acoustic insulation means is a Bragg mirror positioned between the resonant plate and the substrate. The Bragg mirror is here made by a strongly contrasting acoustic impedance layer, for example aluminum nitride or a stack of silicon nitride and silicon oxide layers, which stacks the bulk wave of the expected operating frequency in phase and completely. Configured to reflect.

  In a first step 304, a lithium niobate wafer is prepared so that the initial cut is in the direction of thickness with a first upper surface and a second lower surface,

Represented as:

  In a second step 306, a Bragg mirror is positioned on the top surface of the lithium niobate substrate, and the surface of the mirror is sufficiently wide to insulate a significant number of resonant plates.

  The mirror here is made by a large spreading stack of strongly contrasting acoustic impedance layers, for example aluminum nitride or silicon nitride and silicon oxide layers, which stack the bulk wave of the expected frequency in phase and completely. Configured to reflect.

  The Bragg mirror is attached to the substrate by an adhesive bonding method using pre-deposition of adhesive joints. This mirror then consists of a stack of materials that are transferred according to the method described for FIG. 5 (polymer adhesive bonding, metal diffusion, molecular bonding) and thinned to reach the required thickness, The thickness may vary significantly depending on the target operating frequency. More specifically, for radio frequency applications, the required layer thickness results in a physical or chemical, plasma-assisted deposition in the solid or gas phase, resulting in a stack of layers each within a few micrometers to only 1 μm. It may prove to be compatible with the methods (evaporation, sputtering, chemical vapor deposition, molecular jet, etc.). It is therefore possible to make multiple layers that have a controlled thickness and produce a mirror with a high reflection efficiency close to that of the air gap.

  In a third step 308, a layer of piezoelectric transducer is deposited on a Bragg mirror. The crystal orientation of the transducer has a large electroacoustic coupling coefficient when its layers are cut along the thickness direction of the substrate through two planes that are parallel to each other and have a properly chosen normal direction, It is chosen to be advantageous for generating and maintaining acoustic bulk waves between the cutting planes of the transducer.

  Here, the material is assumed to be the same as the substrate material, ie lithium niobate, and the crystal orientation is the same during stacking. Therefore, electrical converter cutting is

Cutting during cutting of the flat plate,

Is suitable for the required application, i.e. large for wideband filtering, i.e. greater than 5%, and intermediate or moderate for applications using narrowband filters or resonators, i.e. between 5% and 0.0001 Is considered to have a strong electroacoustic coupling coefficient.

  For example, an initial raw slice or wafer is cut into two equal parts, a first part used as a substrate and a second part used as a transducer.

  Attachment of the transducer layer to the Bragg mirror is accomplished using, for example, an adhesive joint.

  In a fourth step 310, similar to the second step 106 of the method 102, the top surface of the lithium niobate wafer forming the transducer is coated with a resin, for example, Shipley brand resin S1828. The resin deposition is carried out over a thickness of 2.5 μm, for example using a spin coating method. In the same step, the resin is annealed at 95 ° C. for 1 hour in an oven to evaporate the solvent and thus make the resin more resistant to the saw cutting step.

  In the fifth step 312, as in the third step 108 of the method 102, one plate or several plates are cut in a stack along a parallel plane, the direction of which is the desired cut,

Corresponding to

  In order to construct a resonant plate sawing, here at least four saw cuts are required to make the plate. In fact, the width of the saw blade is 200 μm so that two superimposed saw cuts will give an accessible gap of 350-400 μm on either side of the plate to allow testing under the probe tip. To be done.

  During the fifth step 312, the thickness e2 and width l of the at least one slab is determined by the depth of the cut and the accuracy of the alignment between the two saw cuts in series and the electrode by the superposition of the two saw cuts. Specified by the width of

  Once the fifth step 312 is performed, a sixth step 314 identical to the fourth step 110 of the method 102 is performed.

  In a seventh step 316, which is the same as the fifth step 112 of the method 102, a metal electrode is deposited.

  Next, in an eighth step 318, the flat plate or bar is coated with the protective resin S1805 using a spray coating technique. This eighth step gives the possibility to cover the structured niobate wafer, ie the chip provided with their electrodes, with a resin.

  The ninth and final step 320 consists of defining the length L of the plate or bar by cutting with a saw, for example in this case in our case 500 mm.

  According to FIG. 13, the first intermediate state 322 of the resonator of FIG. 5 obtained at the end of the second step 306 of the method 302 is a first raw niobic acid intended to form a holding substrate. A lithium wafer 324, a layer 326 forming a Bragg mirror surrounded by two adhesive joints, a second raw lithium niobate wafer 328 intended to form at least one resonant plate after machining, and S1828 is a stack of layers 330 of resin.

  According to FIG. 14, the second intermediate state 332 of the resonator of FIG. 5 obtained at the end of the third sawing step 308 is machined over the substrate block 324 and the layers 326, 328, 330 into the recesses. Or a flat plate 336 surrounded on both sides by exposed or exposed valleys 338, 340. The two end bars 342, 344 of the chip 332 now surround only one flat plate 336. The resin layer 346 is deposited on one upper surface 348 of the flat plate 336, upper surfaces 350 and 352 of the rod-shaped portions 342 and 344, and two band-shaped portions 354 and 356 of recesses positioned on both sides of the flat plate 336.

  According to FIG. 15, the third intermediate state 362 of the resonator of FIG. 1 obtained at the end of the lift-off step for depositing the electrode is a structured chip.

  Here, chip 362 includes a single resonant plate 336 having two electrodes 364, 366 of aluminum on both sides of its two sides, each electrode 364, 366 having an upper surface 348 of plate 336 and a resonant plate 336. It slightly protrudes from a part of the floor surface of the substrate 324 at the bottom of each side surface.

  This structure after cutting off the edge of the substrate corresponds to the structure of the resonator of FIG.

  In general, the method 402 for manufacturing the resonator described in FIGS. 1 to 6 includes three steps 404, 406, 408.

  In a first step 404, an initial resonant flat plate raw layer is prepared, the initial resonant flat plate raw layer is made of a piezoelectric material, and is raw in a raw layer thickness eb and a plane perpendicular to the thickness direction. It has a spatial extent that is clearly greater than the layer thickness eb. The crystal orientation of the raw layer is pre-selected such that the crystallographic cut surface of the raw layer exists in the direction of thickness eb, so that a wafer cut according to the cut surface and having a thickness e2 is Suitable for the required application, ie large for medium or wideband filtering, or greater than 5%, medium or moderate for applications using narrowband filters or resonators, ie between 5% and 0.0001 An included plane-to-plane type piezoelectric resonator in which a bulk wave propagates in the thickness direction of the wafer is generated with an electroacoustic coupling coefficient.

  In a second step 406, the resonant plate is cut out partially or entirely in the thickness direction of the raw layer and at the initial resonant plate raw layer, and the resonant plate has a resonant plate thickness e2 that faces each other. First and second planes, which have a length L and a width l, and the cutting is performed by machining along the direction of the cutting plane, The width l and the thickness of the raw layer are in the same direction, and the material and crystal orientation of the raw layer, the direction of the cutting plane, the length L of the resonant plate, the width l, and the second thickness are It is configured to capture a bulk wave at the operating frequency and produce a piezoelectric resonator having a plane-to-plane bulk wave, ie a bulk wave propagating in the thickness direction of the resonant plane.

  In a third step 408, first and second metal electrodes are deposited at least partially covering the first and second surfaces of the resonant plate, respectively. The respective surfaces of the first and second electrodes are at least partially facing each other through the resonant plate.

The applications used for the resonator described above are as follows.
A resonator for an RF frequency source.
-Resonators and impedance elements for network frequency filters (ladder or trellis type filters).
-Coupled resonators for polar frequency filters (by acting on specific edges of the bars by integrating into them localized cutouts or mass overloads to create mode coupling conditions).
-Resonators for sensors and in particular wireless sensors that may be interrogated through the IFM (industrial-scientific-medical) band.
- resonator for the high-temperature sensor (langanite and derivatives thereof, GaPO _4, ZnO or bulk AlN, to materials such as etc.).
-Resonators for acceleration measurement, gyroscope and gravity measurement sensors.
An element for modulating an optical signal by acousto-optic coupling.

Materials that may be utilized for these operations are lithium niobate, lithium tantalate and potassium niobate for filters with strong bonds and (potentially piezoelectric ceramics and relaxed ceramic single crystals) , Quartz, lithium tetraborate, gallium orthophosphate (GaPO ₄ ), langasite (La ₃ Ga ₅ SiO ₁₄ ) and many variants thereof (langanate, langanite, etc.) and single crystal forms Materials that are more delicate, but whose piezoelectric properties are advantageous for bulk acoustic wave applications, namely aluminum nitride (AlN) or zinc oxide (ZnO). For sensors, especially for high temperature sensors (suitable electrodes selected for this type of application, ie platinum, iridium, zirconium or rubidium or high temperature and robustness obtained for example by alloying the materials mentioned above. As well as any other electrode known to be, and optionally other metal bodies or metal oxides with a conductivity comparable to those of the ideal metal and a proven stability of said properties versus temperature), as shown Generally thick enough to allow machining of the rods (minimum amount of 200 μm in raw form, or several tens of microns if transferred on the substrate according to the method described above) Amount) Any piezoelectric single crystal available in flat plate form.

  The improvement in spectral purity also passes the optimization of the horizontal arrangement of the rods, especially by breaking the conditions for radial resonance and eliminating the rod mode by apodization of the rod shape, the latter being To avoid having a uniform thickness that may facilitate such modes, it may be performed on the initial wafer, for example by corrugation or chemical cutting.

  For lithium niobate and lithium tantalate, it is possible to reduce the temperature sensitivity of the resonator by covering the resonator with a deposit of amorphous silica, the temperature coefficient of frequency is a positive sign, Gives the possibility to compensate for the negative sign of the temperature coefficient. The deposition may advantageously be performed on the electrode, for example by sputtering, so as not to produce any parasitic capacitance if the silica deposit is to occur before metallization.

Some examples of material cutting currently most used for bulk wave applications should be recalled as follows.
In the case of quartz, (YX1) / 40 ° (± 5 °) for using BT cutting, (YX1) / − 54 ° (± 5 °) for using AT cutting, to utilize SC cutting (YXwl) / 22 ° / 46 ° (± 5 ° for each angle).
-In the case of lithium niobate, the excitation of pure transverse bulk waves (YXI) / 126 ° (± 5 °) to exploit cutting (YXl) / 36 ° which only allows excitation of pure longitudinal bulk waves The same crystal orientation for lithium tantalate, (YX1) / 73 ° (± 5 °) to utilize cutting (YX1) / 163 ° which only allows.

  Therefore, for a given surface, in terms of electromechanical coupling for frequency filter applications, in terms of temperature stability for applications using stable frequency sources, stress for sensor applications. From the point of view of sensitivity to, the number of resonators can be reduced by combining these various characteristics to produce a given application function, typically by utilizing the more advantageous single crystal cutting cut. It can be increased by at least 10 times.

DESCRIPTION OF SYMBOLS 2 Resonator 4 Substrate block 6 Resonance flat plate 8 1st surface 10 2nd surface 12 1st metal electrode 14 2nd metal electrode 16 Plane 20 Electrical excitation source 22 Extraction circuit 32 Resonator 36 Resonance plate 38 Contraction area 42 first electrode 44 second electrode 54 first electrode 56 second electrode 58 bulge 60 bulge 62 resonator 64 substrate block 66 resonance plate 68 coupling element 72 resonator 74 substrate block 76 resonance plate 78 acoustic insulation element 102 Method 202 First intermediate state 204 Resin layer 206 Raw wafer 212 Second intermediate state 214 Block, substrate 216 Resonant flat plate, flat plate 218 Valley portion 220 Valley portion 222 Rod-shaped portion 224 Rod-shaped portion 226 Resin layer 228 Upper surface 230 Upper surface 232 Upper surface 234 Band 236 Band 242 Third intermediate state, chip 244 Electric Pole 246 Electrode 252 Chip 254 Resonator 256 Resonator 258 Resonator 264 Resonant flat plate 266 Resonant flat plate 268 Resonant flat plate 270 Electrode 272 Common substrate floor 276 Insulating strip 302 Method 322 First intermediate state 324 First raw wafer, substrate block 326 Layer for forming Bragg mirror 328 Second raw wafer 330 Resin layer 332 Second intermediate state, chip 336 flat plate, resonant flat plate 338 Valley 340 Valley 342 Rod 344 Rod 346 Resin layer 348 Upper surface 350 Upper surface 352 Upper surface 354 Strip 356 Strip 362 Third intermediate state, chip 364 Electrode 366 Electrode 402 Method e1 Substrate thickness e2 Resonance plate thickness e21 Resonance plate thickness e22 Resonance plate thickness e23 Resonance plate thickness L Resonant plate length l The width of the flat plate

Claims (8)

A substrate block (4) as a holding means, which operates at a predetermined frequency, has a plane (16), has a first thickness (e1) along the normal of the plane, and is made of a first material. 64, 74),
Has a first plane (8) and the second plane (10) positioned facing each other, have a length (L), width (l) and the second thickness (e2), piezoelectric A resonant plate (6, 36, 66, 76) made of a second material ,
The resonant flat plate (6, 36, 66, 76) covers at least partially the first plane (8) and the second plane (10), respectively, and the resonant flat plate (6, 36, 66, 76). A bulk wave piezoelectric resonator comprising a first metal electrode and a second metal electrode (12, 14, 42, 44, 54, 56) located at least partially facing each other through
The resonance plate (6, 36, 66, 76) has the same direction as the width of the resonance plate (6, 36, 66, 76) and the first thickness of the substrate block (4, 64, 74). Vertically attached near the plane (16) of the substrate block (4, 64, 74) to have
The first material, the second material, the first thickness of the substrate block (4, 64, 74), the length (L) of the resonant plate (6, 36, 66, 76 ) , The width (l) and the second thickness (e2) capture the bulk wave at the operating frequency of the resonator, and the plane-plane type, ie the bulk wave is the second thickness of the resonant plate. is configured to produce a mold that propagate in the direction of the bulk wave piezoelectric resonator,
Attachment elements and / or acoustics of an operating frequency (f) different from the substrate block (64, 74) and the resonant plate (66, 76) made of at least a third material different from the first and second materials Comprising an insulating element (68, 78), said attachment element and / or acoustic insulating element (68, 78) comprising a Bragg mirror formed by a single adhesive layer, a stack of layers with contrasting acoustic impedances A bulk wave piezoelectric resonator characterized by being included in a group . A lateral shape defined as a ratio of the width (l) of the resonant plate (6, 36, 66, 76) to the second thickness (e2) of the resonant plate (6, 36, 66, 76). The bulk wave piezoelectric resonator according to claim 1, wherein the factor (Fl) is 5 or more, preferably 10 or more.   The longitudinal form factor defined as the ratio of the length of the resonant plate (6, 36, 66, 76) to the thickness of the resonant plate (6, 36, 66, 76) is 5 or more, preferably The bulk wave piezoelectric resonator according to claim 1, wherein the bulk wave piezoelectric resonator is 10 or more.   The bulk acoustic wave resonator according to claim 1 or 2, wherein the resonant plate (6) and the substrate block (4) are made of the same piezoelectric material and integrally form a component. The resonant plate (6, 76) and the substrate block (4, 74) are made of the same piezoelectric material,
The crystallographic cut of the resonant plate (6, 76) along a plane parallel to both of its surfaces indicates that the electroacoustic coupling coefficient of the transducer formed by the resonant plate is equal to the thickness of the resonant plate. 5. A piezoelectric resonator according to any one of the preceding claims , selected to be greater than 0.0001 for bulk waves propagating in the direction. The resonant plate (36) has a contraction region (38) throughout its length in the thickness direction, so that the thickness of the resonant plate (36) passes a minimum amount and the resonance When the flat plate (36) is attached to the substrate block (4), the shrinkage area (38), characterized in that located near the plane of the substrate block (4), claims 1 to 5, The piezoelectric resonator according to any one of the above. Said first material, potassium lithium niobate, lithium tantalate, niobate, a piezoelectric ceramic, quartz, lithium tetraborate, gallium orthophosphate, langasite, Rangateito, langanite, selected from zinc oxide and aluminum nitride,
It said second material is selected, lithium niobate, lithium tantalate, potassium niobate, a piezoelectric ceramic, quartz, lithium tetraborate, gallium orthophosphate, langasite, Rangateito, langanite, diamond carbon, silicon, and sapphire The piezoelectric resonator according to any one of claims 1 to 6 , wherein: The metal electrodes (12, 14, 42, 44, 54, 56) are made of aluminum, copper, titanium, platinum, iridium, zirconium, rubidium, molybdenum, nickel, tungsten, gold, polysilicon, and various metals thereof . Made of materials selected from alloys,
Their thickness is distributed so as to obtain a mass distribution localized to the boundary of the resonant flat and the substrate block in order to gather to capture the bulk wave within a localized area of the resonant plates, claim The piezoelectric resonator according to any one of 1 to 7 .

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